The most useful stage lamp for use in theatrical and related lighting is the ellipsoidal lamp. As is well known, an ellipse has two foci. Once such an ellipse is rotated 180°, the boundaries of the ellipse trace a three-dimensional figure known as an ellipsoid. Overall, the ellipsoid is egg-shaped with each of its foci disposed along the major axis of the ellipsoid at opposite ends of the egg. Understanding this three-dimensional geometry of an ellipsoid is important in understanding the optical function of an ellipsoidal stage lamp.
In a so-called ellipsoidal lamp, a reflector having an ellipsoid shape at one end of the ellipsoid is used to project light from the stage lamp. A light is placed with its filament at the focus of the ellipsoidal reflector. Light is projected by the ellipsoidal reflector to and towards the second focus of the ellipsoid. Since the second focus of the ellipsoid is located at an effective image plane, objects placed at the image plane will be projected by the lamp with reasonable definition for essentially the full “throw” or range of the stage lamp.
The second end of the ellipsoid of an ellipsoidal stage lamp is open. Light to be projected from the lamp is intercepted by projecting lenses at the open portion of the ellipsoid. Typically, the projecting lenses are given some excursion along the optical axis (major axis of the ellipsoid) with respect to the opening of the ellipsoid. This excursion allows the beam projected from the ellipsoidal stage lamp to be focused at the end of its throw (or light-projecting range) to provide the desired lighting effect. For example, where areas are being discreetly lit by an array of ellipsoidal lamps, it is often desired that the borders of illumination of the lamp be slightly out of focus or “soft.” Alternatively, where “hard” borders are desired, such as lighting a small interior volume of the stage (for example a room with one wall open to the audience), the barrel focusing the projected beam can be given a sharp border.
Most commonly, shutters are placed at the second focus of the ellipsoid for controlling the borders of illumination projected from the ellipsoidal stage lamp. This enables a light designer to precisely trim the beam at its destination, which, in the case of a stage, is usually an area or volume to have a particular lighting effect.
Interestingly enough, the borders are optically reversed. For example, the top shutter trims the bottom border of the projected beam. Similarly, the right shutter trims the left border of the projected beam. This optical reversal applies to all borders and images projected from the second focus of the ellipsoidal stage light.
It is also known to project special patterns from ellipsoidal stage lamps. Many such patterns are intricately stamped out of metal sheeting, with the specific patterning desired projected on an incident stage surface, such as the cyclorama curtain commonly hung at the back of the stage. Gobos are typically static patterns placed in ellipsoidal lamps at the second focus to project patterns; they do not impart a moving effect to the projected light.
One of the most popular ellipsoidal lamps is manufactured by the Electronic Theater Controls Corp. of Middletown Wis. and sold under the trademark “Source IV.” It is the use of the Source IV that constitutes the preferred embodiment of this invention.
In modern ellipsoidal lamp construction, the reflector and light-holding base are typically mounted to a yoke. Next, a shutter assembly and barrel are mounted over the light-holding base. Finally, a telescoping lens assembly is mounted for beam focus within the barrel. By moving the telescoping lens assembly relative to the remainder of the lamp, the projected beam can be focused, as it is incident upon its target.
As anyone who has been to the theater can attest, ellipsoidal lamps are typically mounted in tightly spaced rows and columns. The most common mounting of such lamps is in “balcony trees” where the lamps have an optimal angle with respect to the stage. It is to such a mounting of ellipsoidal lamps that this invention is especially directed.
Lighting designers use optically projected special lighting effects such as clouds, fire, rain, sleet, snow and the like. In the projection of such special lighting effects, an instrument known as a “projector” is typically employed. In such a projector, a light interior of the instrument projects the light to a focal plane. At the focal plane there is provided a medium of some kind to project the desired effect. For example, where clouds are desired, a horizontally moving reel can be used with elongate and irregular apertures in the reel. For fire, a similar reel moving in a vertically upward direction is used. For rain and snow, movement of the reels is in a generally downward direction. Alternately, rotating wheels having desired patterns to be projected can be used. Simply stated, patterns projected by modern stage projectors are limited only by the imagination of the lighting designer.
Because of their mechanical complication, projectors are usually large expensive instruments. Their mounting is far from simple. Because of their weight and mechanical/complexity, such projectors usually must be reserved to specially select mounting locations, such as a special portion of the balcony tree. Alternatively, the projectors can be placed within arrays of the ellipsoidal stage lamps provided; then almost all of the surrounding stage lamps are remounted and refocused.
Attempts have been made to modify conventional lighting instruments, such as ellipsoidal theatrical lamps, to accommodate projection of special effects. Typically, a conventional lamp is permanently altered and thereafter becomes part of a specialized projector. Again, because of size and mechanical complication, special mounting of the resulting instrument is required. Further, the altered ellipsoidal theatrical lamp can never be recovered for conventional use. After its alteration into a projector, the lamp is dedicated to its projector function and leaves the ordinary inventory of stage lighting instruments.
In Kleeman et al., U.S. patent application Ser. No. 09/672,586, filed Sep. 28, 2000, and entitled Linear Moving Pattern for Ellipsoidal Type Stage Light, a gobo-type pattern for placement within the drop-in iris slot of an ellipsoidal stage lamp is disclosed. While this instrument is useful in certain situations, the narrow confines of the iris slot give this instrument-restricted applicability. Further, this specialized instrument requires that the projecting reel be narrowed or “necked down” in order for the effect to occur within the iris aperture.